This invention relates to switching device for detecting the rotational positions of a rotary shaft, and more particularly it is concerned with a switching device suitable for use in detecting whether or not the rotational position of an objective to be detected, such as a throttle valve of an internal combustion engine, has reached a predetermined location.
A switching device of one type known in the art for detecting the rotational positions of a throttle valve is adapted to be rotated by a rotary shaft of the throttle valve and comprises a rotor formed with a guide groove, and three plate springs each having an electrical contact at the forward end. The electrical contact of the center plate spring acting as a movable contact is guided by the guide groove, and the electrical contacts of the rest of the plate springs are fixed contacts.
In this type of switching device of the prior art for detecting the rotational positions of a throttle valve, when the rotary shaft rotates and its rotational position reaches a predetermined position, such as an idling position, the movable contact is brought into contact with one fixed contact and a signal is generated. When further rotation of the rotary shaft brings the shaft to another predetermined position, such as a full loaded position, then the movable contact is brought into engagement with the other fixed contact, thereby generating another signal.
In this device of the prior art, since the actuation of the contacts brought about by the rotation of the rotary shaft is governed by the guide groove, the design of the rotor is a limiting factor, and the guide groove is required to be formed with a high degree of dimensional accuracy. In addition, final adjusting step is required in fabricating such device. With the detecting device of this construction, difficulties are experienced in detecting a vary small deviation in angle (less than 1.5.degree., for example) from the full open position of the throttle valve.
In another type of roatational position detecting device known in the art, there is provided a rotor rotated by a lever rotated as a unit with the rotary shaft of the throttle valve, with a certain degree of hysteresis between the lever and the rotor. The lever has on one side thereof a plate spring mounting a fixed contact and a plate spring mounting a movable contact for detecting an idling position, and a fixed body is secured to a base plate. The lever has on the other side thereof a plate spring mounting a movable contact and a plate spring mounting a fixed contact for detecting a loaded position which are secured to the rotor. The rotor is provided with three sliders formed of plate spring.
In this device of the prior art, one set of contacts are opened when the rotary shaft has rotated to a predetermined position, and a signal indicating the idling position is generated. Further rotation of the rotary shaft closes the other set of contacts and generates an acceleration pulse signal. Still further rotation generates a signal indicating the full loaded position.
Some disadvantages are associated with this type of detecting device. Difficulties are experienced in adjusting the operation angle, particularly adjusting the detection angle for the idling position. Also, this device raises a problem with regard to resistance to vibration. More specifically, when the device suffers vibration as a whole, the plate springs might vibrate and actuate the contacts even if the lever has not rotated to a predetermined position, thereby inadvertently generating a signal by misoperation Also, the device is complex in construction and its parts are large in number.